Stomata , Leaf Water-content , and Wilting of Plants. 383 
The commencement of wilting may be inferred from the flaccid condition 
of the leaves before it is possible to determine experimentally a definite 
decrease in leaf water-content. 
The loss of leaf turgidity following such a small decrease in leaf water- 
content indicates that the wall of a normally turgid cell is only slightly 
distended. 
The water-contents of leaves apparently similar may differ by as much 
as 2 per cent, in Eupatorium adenophorum , and more in other species. 
The diurnal change in leaf water-content in south-eastern England 
amounts to less than 2 per cent., much less than the maximum variation 
(8 per cent.) previously recorded for desert habitats. 
Literature cited. 
1. Bakke, A. L. : The Index of Foliar Transpiring Power as an Indicator of Permanent Wilting 
in Plants. Bot. Gaz., t 91 5, lx. 314-19. 
2. — : Determination of Wilting. Bot. Gaz., 1918, Ixvi. 81-116. 
8. Blackman, V. H., and Knight, R. C. : A Method of Controlling the Rate of Air Movement 
in Transpiration Experiments. Ann. Bot., 1917, xxxi. 217-20. 
4. Briggs, L. J., and Shantz, H. L. : Comparison of the Hourly Evaporation Rate of Atmometers 
and Free Water Surfaces with Transpiration Rate of Medicago sativa. Journ. Agr. Res., 
1917, ix. 277-92. 
5. Clark, Arabel W. : Seasonal Variation in Water Content and in Transpiration of Leaves of 
Fagus americana , Hamamelis virginiana, and Quercus alba. Contrib. from the Bot. Lab. 
Univ. Pennsyl., 1916, iv. 105-43. 
6. Cribbs, J. E. : Ecology of Till a americana. I. Comparative Studies of Foliar Transpiring 
Power. Bot. Gaz., 1919, lxviii. 262-86. 
7. Darwin, F. : Observations on Stomata. Phil. Trans., B., 1898, cxc. 548. 
8. : A Self-recording Method applied to Movements of Stomata. Bot. Gaz., 1904, 
xxxvii. 89. 
9. , and Pertz, D. F. M. : New Method of estimating the Aperture of Stomata. 
Proc. Roy. Soc., B., 1911, lxxxiv. 149. 
10. Dixon, H, H.: Transpiration and the Ascent of Sap in Plants. Macmillan, 1914. 
11. Farmer, J. B. : On the Quantitative Differences in the Water Conductivity of Wood in Trees 
and Shrubs. Part II. Deciduous Plants. Proc. Royal Soc., B., 1918, xc. 232-50. 
12. Gray, J., and Peirce, G. J. : The Influence of Light upon the Action of Stomata and its 
Relation to the Transpiration of Certain Grains. Amer. Journ. Bot., 1919, vi. 131-55. 
13. Knight, R. C. : ‘Relative Transpiration’ as a Measure of the Intrinsic Transpiring Power of 
the Plant. Ann. Bot., 1917, xxxi. 351-59. 
14. : On the Use of the Porometer in Stomatal Investigation. Ibid., 1916, xxx. 57. 
15. : Recent Work on Transpiration. New Phytol., 1917, xvi. 129-39. 
16. Laidlaw, C. G. P., and Knight, R. C. : A Description of a Recording Porometer and a Note 
on Stomatal Behaviour during Wilting. Ann. Bot., 1916, xxx. 47-56. 
17. Livingston, B. E., and Brown, W. H. : Relation of the Daily March of Transpiration to 
Variations in the Water Content of Foliage Leaves. Bot. Gaz., 1912, liii. 309-30. 
18. Neger, F. W. : Die Wegsamkeit der Laubblatter fur Gase. Festschr. Z. E. Stahl., 19 1 8, 152-61. 
19. Shreve, E. B. : Daily March of Transpiration in a Desert Perennial. Carn. Inst. Publ., 1914, 
No. 201. 
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